In general, a thin film transistor includes a source electrode, a drain electrode, a gate electrode, a semiconductor layer, an insulating layer, and a substrate.
A method of manufacturing a known transparent thin film transistor includes forming a semiconductor layer on a gate electrode of ITO or IZO by using a channel material such as ZnO, ZnO:Al, InZnO, ZnO:Sn, ZnO:Ga:In, and depositing the channel material or the electrode material to form source/drain electrodes. However, in the method of manufacturing the thin film transistor, the materials are very easily etched during wet etching that may be used during the etching process, and in particular, IZO having an amorphous configuration is etched in an even higher etching amount. Accordingly, in the case of when the IZO is used as the source/drain electrodes, in the etching process used in the manufacturing of the thin film transistor, since an etching selectivity of the electrode and the semiconductor layer channel is hardly present in the wet etching, many problems may occur. Accordingly, the thin film transistor is mainly manufactured by using a lift-off process.
However, the lift-off process has serious problems such as the occurrence of overhang structure due to two photoprocesses, the generation of impurity due to the deposition process in a state in which a photoresist is present, and an increase in production cost due to an additional photoprocess. Therefore, the process may be a very undesirable process that cannot be applied to a process of manufacturing a thin film transistor.
In addition to the typical process of manufacturing the thin film transistor, there is a process of additionally depositing a SiN channel protective layer on a semiconductor layer. However, this has problems in that since a channel photomask is additionally used, the manufacturing cost of the thin film transistor is increased. In addition, there is a process of controlling only an etching time without the etching selectivity during an etching process to etch the source/drain electrodes according to an etching amount. However, in this process, since the etching selectivity is not present, there is a problem in that it is very difficult to control the etching. Accordingly, it is not a desirable process of manufacturing the thin film transistor.